The present invention is concerned with a hydraulic brake system including an anti-locking control, in particular for use with automotive vehicles,.
A brake system of the afore-mentioned type is disclosed in German Patent Application No. P 40 15 882 which is concerned with a so-called closed anti-locking control system (ASS) which, as opposed to the state-of-the-art open anti-locking control systems, does not have a direct connection of the auxiliary pressure and return-flow system to the non-pressurized supply tank provided on the master cylinder side. The auxiliary pressure system, during the brake slip control, withdraws from the low-pressure accumulator disposed on the return-flow conduit to the pump the required pressure fluid volume, conveying the same to the master cylinder pressure conduit. At the same time, excess pressure fluid is supplied to a high-pressure accumulator provided in the branch conduit leading to the auxiliary pressure conduit, with the pressure level of the high pressure accumulator being adjusted through a pressure relief valve coupled thereto. In response to the electromagnetic actuation of the inlet and outlet valves disposed in the master pressure conduit and the return conduit, the anti-locking control is then effected in the associated wheel brakes.
The circuit configuration involved does not enable the afore-described brake system to control the start-up and traction slip, respectively. Actuation of the pump in response to traction slip, inevitably, would result, as a consequence of the pedal being in the release position, in a return flow of pressure fluid to the supply tank rather than to the wheel brake.
It is, therefore, the object of the present invention to improve a brake system having the afore-described features so as to enable, by substantially preserving the basic circuit configuration, in particular, the control system, a low-cost improvement of the traction slip control with no need for enhancing the electronic controls of the brake system.